1. Field of the Invention
The present invention relates to a floating head for use with a recording apparatus of magneto-optical memory type. More particularly, the present invention relates to an improved floating head with which a vertical magnetic field can be efficiently concentrated on an optical recording medium at the focusing point of converging light.
2. Description of the Related Art
The principle of recording and erasure with an apparatus of magneto-optical memory type is described below with reference to FIGS. 1(A)-1(C). As shown in FIG. 1(A), a recording film a made of a magnetic material is illuminated with a spot of laser beam, with a magnetic field being applied in the direction indicated by fine arrows; whereupon the direction of magnetization in the illuminated area is reversed to change the polarization angle resulting from the Kerr effect, with the resulting change being used to record and reproduce information of interest (see FIG. 1(B)). When a spot of laser beam is applied to the recording area of film a, with a magnetic field being applied in a direction opposite the direction in the recording mode as shown in FIG. 1(C), whereupon the direction of magnetization in the illuminated area is restored to the initial state so as to erase the recorded information.
An optical head is necessary to record, reproduce and erase information in the recording apparatus of magneto-optical memory type and it is known to use a floating head as described in Japanese Patent Application Unexamined Publication No. Sho. 60-261052. As shown in FIGS. 2-4, the main part of a floating head generally indicated by b comprises an air slider that is formed of a soft magnetic material and which is made afloat by an air stream produced by the rotation of an optical recording medium c, a prism b2 that is installed on the air slider b1 and which permits laser light from a light source d such as a semiconductor laser to be reflected toward the recording medium c, an objective lens b4 that is fitted in an optical path forming aperture in the air slider b1 and which permits the reflected laser light from the prism b2 to converge on the focusing plane of the recording medium c, and turns of a coil b6 that are placed within a groove b5 formed around the aperture b3 on the side of the air slider b1 that is the closer to the recording medium c and which form a generally perpendicular magnetic field with respect to the focusing plane of the recording medium c. The head is provided in the vicinity of the recording medium c and supported with a suspension in spring form b7 that is moved radially of the recording medium c by means of a drive unit e.
The floating head b which has a minimum number of components including the prism b2, objective lens b4 and coil b6 mounted on the air slider b1 has the advantages of light weight and shorter access time. Further, the air slider b1 which is made afloat by an air stream created by the rotation of the recording medium c is capable of maintaining a constant distance from the recording medium c, thereby eliminating the need of using a mechanism for focusing the laser light passing through the objective lens b4.
The floating head b described above has several disadvantages. Since the air slider b1 is totally made of a soft magnetic material, magnetic paths are formed on opposite sides of the coil b6 as shown in FIGS. 5 and 6, with one magnetic path being formed on the side of the air slider b1 that is the closer to the aperture b3 and the other on the far side of the slider, and this makes it difficult to concentrate, via air, the generated magnetic field on the recording medium c at the focusing point .alpha. of laser light. As a result, an extremely great magnetizing force has to be applied to produce a magnetic field of 200-300 Oe on the focusing plane of the recording medium c that is necessary to perform effective magneto-optical recording or erasure. Conventionally, this need has been met by increasing the number of turns of the coil b6. However, as the number of turns of the coil b6 is increased, its self-inductance also increases to make it difficult to reverse the direction of an applied magnetic field at high speed for image recording or erasure and this has led to a slower recording or rewriting speed.
As described in Japanese Patent Application Unexamined Publication No. Sho. 61-71437, the concentration of a vertical magnetic field may be enhanced by providing a soft magnetic layer on the underside of the recording film in the optical recording medium so as to form magnetic paths between the soft magnetic layer and the coil. However, this idea has proved still insufficient to concentrate a magnetic field toward the point on the recording medium of which laser light is to be focused.